Decreasing the Cost of Flooding
Accurate flood maps can save property and lives in landscape
By James L. Sipes, ASLA, and Kimberly A. Sipes
C/O FEMA And Denver Urban Drainage and Flood Control District
Floods inflict more damage and economic losses on the United
States than any other natural disaster. Perhaps one reason is that more than 30
million Americans live in areas that have a high risk of flooding.
During the 10 years from October 1992 through October 2001,
flooding caused more than 900 deaths and resulted in approximately $55 billion
in damages. The greatest loss was in 2005, when loss payments totaled $17.4
billion, in large part because of flooding caused by hurricanes Katrina, Rita,
Limitations with Flood Mapping
Why is flooding such a big problem? One reason is that
Federal Emergency Management Agency (FEMA) flood maps, which are intended to
define areas that are “safe” from flooding, are outdated and inaccurate. Flood
maps have been produced and used for 35 years, and many have not been updated in
years. According to FEMA, nearly 70 percent of the nation’s approximately
92,222 flood maps are more than 10 years old, and many of these maps no longer
accurately reflect current flood hazard risks. As a result, development is
occurring in areas that should be restricted because of flooding hazards. FEMA
made an effort to transfer its paper maps to digital format in the 1990s,
creating what’s known as the Q3 flood data. This Q3 data has been the
foundation for many design and planning decisions over the years. But landscape
architects using Q3 flood data are using outdated information.
To be blunt, there are many problems associated with Q3
flood data. The horizontal control of Q3 flood data is consistent with that
used for 1:24000 scale maps, which is acceptable for community and regional
scale planning projects but is not useful for site-scale projects.
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